Elbow pinning for supracondylar humerus fractures is a daily occurrence in large pediatric orthopedic centers. The common fracture pattern happens when children and adolescents attempt to stop a fall and the elbow hyperextends, separating the supportive muscle from the bone and creating a fracture across the supracondylar region. In up to half of all children, the arm fractures at an oblique angle that can be challenging to immobilize with normal pinning strategies. Thankfully, researchers have uncovered a simple solution: use a bigger wire.
“For this type of fracture, surgeons are usually putting in about three wires,” says Christopher Iobst, MD, pediatric orthopedic surgeon and director of the Center for Limb Lengthening and Reconstruction at Nationwide Children’s Hospital. He is also lead author on the study, published in Journal of Orthopaedic Trauma. “In the process of putting those in, sometimes you get one that bounces and you need to redirect your hand to put the wire in at a better angle.”
Small diameter (1.6 mm) k-wire is typically used in young patients to pin the elbow in place for proper healing. However, the thin wire is flexible and may not penetrate the second cortex when used at steep oblique angles, which causes the wire to bend or “bounce” up the medullary canal. Without getting the wire through the outer edge of the elbow bone (the far cortex), the fracture’s fixation can be unstable. To address the problem, surgeons have to reposition and redrill to place a new pin, but viable drilling locations can be limited, making it very desirable to get a firm anchor with the wire on the first attempt.
To study a possible option to avoid k-wire bounce and repeated drilling, researchers compared the maximal angles at which 1.6 mm and 2.0 mm k-wire (the next size up and a stiffer, stronger option) would penetrate the far cortex. The team used three intact cadaver elbows and a specialized jig to standardize drilling from the lateral side of the distal humerus at gradually increasing oblique angles until they could no longer get the wire all the way through the bone.
The average maximum angle at which the 1.6-mm k-wire could reliably drill all the way through to the other side was 67 degrees, while the 2.0-mm wire averaged 74 degrees. The difference was statistically significant, suggesting that the thicker wire could be useful for getting secure fixation in elbow fractures that require oblique pin placement.
“We found that if we just increased the diameter of the wire a very small amount, it allowed us to have enough rigidity to avoid the bounce — we could put the pins in at larger angles and accomplish fixation of the fracture,” says Dr. Iobst. “It’s a helpful little technique tip about choosing a slightly larger diameter wire. Most orthopedic surgeons don’t think about just exchanging the wire for a bigger size, but this is an easy thing to do during surgery.”
The researchers recommend that when preoperative evaluation of the fracture suggests the wire’s entry angle will exceed 67 degrees, a 2.0 mm k-wire would be a better option for stabilizing the bone. In cases where the difficulty of fixation is not discovered until after a bounce occurs, Dr. Iobst suggests simply switching to a 2.0 mm wire for the next attempt.
The study was completed during Dr. Iobst’s tenure at Nemours Children’s Hospital. In his biomechanics laboratory within the Center for Limb Lengthening and Reconstruction at Nationwide Children’s, Dr. Iobst continues to study the biomechanics of external fixators for further opportunities to improve fixation stability for limb fractures, deformities and length discrepancy therapies.
Iobst C, Thompson RG, Grauer J, Wheeler P. How to prevent k-wire bounce in oblique supracondylar humerus fractures. Journal of Orthopaedic Trauma. 2018 Dec; 32(12): e492-e496.